Motor vehicles typically have a bumper structure supported on a body of the motor vehicle by energy absorbers that convert into work a portion of the kinetic energy of a force on the bumper structure. Such bumper energy absorbers may include relatively movable structural elements attached to the body and the bumper structure and a resistance medium between the structural elements.
Extendable bumper systems may include an actuator forming part of the bumper energy absorber for extending and retracting the bumper structure. Typically, these systems support the bumper structure close to the body of the motor vehicle during certain conditions, such as when the vehicle is being parked, and extend the bumper structure from the body during other conditions to increase the ability of the bumper energy absorbers to convert the kinetic energy of a force on the bumper structure into work.